This invention relates to a tension member for belt, method of producing a tension member for belt and various kinds of belts such as a synchronous belt, a V-belt, a flat belt and a variable speed belt using the above-mentioned tension member.
A glass cord is generally used as a tension member for power transmission belt such as a synchronous belt to increase the strength of the belt and improve the toughness or the dimensional stability of the belt. For example, in a power transmission belt used for driving an overhead cam (OHC) of an automobile engine, a cord designated as ECG150-3/13 is generally used as a tension member. The ECG150-3/13 cord is obtained in a way of parallel-arranging three glass fiber strands each composed of 200 fibers having a fiber diameter of 9 .mu.m, primary-twisting them into a primary twist yarn, parallel-arranging 13 primary twist yarns and final-twisting them. In short, the tension member has undergone primary twist and final twist.
Such a tension member is fabricated using glass fiber strands treated with resorcine formaldehyde rubber latex (RFL) in order to improve the adhesive strength of the tension member with the rubber belt body (See Japanese Patent Publication No. 3-42290, Japanese Patent Application Laid-Open No. 4-59640 or Japanese Patent Application Laid-Open No. 4-50144). In detail, the glass fiber strands are dipped in an RFL liquid, are returned from the liquid, are dried by heating and are then subjected to primary twist and final twist.
Meanwhile, in view of the recent tendency of increase in temperature around an automobile engine, there has been applied to rubber for automobile engine belt hydrogenated nitrile rubber having the heat resistance more excellent than chloroprene rubber conventionally used. Hydrogenated nitrile rubber has poor adhesive strength as compared with other kinds of rubber materials. Therefore, there is also proposed a technique that a rubber cement is further applied to the above-mentioned final twist yarn (See Japanese Patent Application Laid-Open No. 2-4715 or Japanese Patent Application Laid-Open No. 3-170534).
Further, there is also proposed a technique that hydrogenated nitrile rubber (H-NBR) latex having excellent heat resistance and small water absorbing property is used as latex of the above-mentioned RFL liquid (See Japanese Patent Application Laid-Open No. 63-270877).